Driver for and method of installing foundation elements and a kit of parts for assembling a driver

ABSTRACT

The invention pertains to a driver ( 1 ) for installing foundation elements, such as anchors or piles, in a ground formation and preferably in submerged condition, comprising a housing for accommodating and guiding a weight, an element for mounting the driver ( 1 ) on or in the foundation element, one or more chambers for holding a charge or one or more connectors for connecting the driver ( 1 ) to a source of a high pressure gas, and corresponding conduits allowing a high pressure gas to flow from the chamber(s) or connector(s) to below the weight. The housing is adapted to allow a stroke of the weight having a length such that, during upward movement of the weight the pressure of the gas drops to a value, which will cause the weight to decelerate.

The invention pertains to a driver for installing foundation elements, such as anchors or piles, in a ground formation and preferably in submerged condition, comprising a housing for accommodating and guiding a weight, an element for mounting the driver on or in a foundation element, one or more connectors for connecting the driver to a source of a high pressure gas or, preferably, one or more chambers for holding a charge, and corresponding conduits allowing a high pressure gas to flow from the chamber(s) or connector(s) to below the weight. The invention also relates to a kit of parts for assembling a driver and to a method of installing foundation elements.

Drivers for installing foundation elements are generally known, e.g. from international patent application WO 00/06834, which relates to a tool for use in submerged condition. In WO 00/06834, a hammer body is fixedly supported in axial alignment with the head of a pile that is to be driven and carries a reaction body guided for movement thereon in a direction that is axial to the pile. The hammer body and reaction body define opposed first and second ends of an expansion chamber. A pyrotechnic charge is initiated to create a rapidly expanding volume of high pressure gas in the expansion chamber to generate a downward pressure force pulse to drive the pile, an equal and opposite upward pressure force pulse being applied to the reaction body. A damping structure, preferably a large volume container, operatively associated with the reaction body interacts with the water in which the tool is submerged using the inertia of the water to resist upward movement of reaction body. When the reaction body has stopped moving upwards, it descends back to the start position and applies a secondary blow to the pile.

It is an object of the present invention to improve the driver according to the opening paragraph.

To this end, the driver according to the present invention is characterised in that the housing is adapted to allow a stroke of the weight having a length such that, during upward movement of the weight (and downward movement of the foundation element), the pressure of the gas drops to a value, which will cause the weight to decelerate.

By using the gas not just to accelerate but also to decelerate the impact weight, a voluminous and heavy damping structure is in principle not required and the driver can be built relatively slender and kept relatively lightweight.

It is preferred that the housing is adapted to allow a stroke of the weight of at least 2 meters, preferably at least 5 meters, more preferably at least 10 meters. In practice, the stroke of the weight will not be longer than 50 meters, preferably not longer than 25 meters. The stroke will depend on the pressure above the weight.

The driver according to the invention can be equipped with a solid weight or, especially in a submerged condition, can use a liquid weight, typically (sea)water taken from the surroundings, as will be explained in more detail below.

The invention also relates to a kit of parts for assembling a driver for installing foundation elements, such as anchors or piles, in a ground formation and preferably in submerged condition, comprising two or more segments for assembling a housing of a selectable length for accommodating and guiding a weight, an element for mounting the assembled driver on or in a foundation element, and a section comprising one or more chambers for holding a charge and/or one or more connectors for connecting the driver to a source of a high pressure gas, and corresponding conduits allowing a high pressure gas to flow from the chamber(s) or connector(s) to below the weight. It is preferred that the total length of the segments is at least 2 meters, preferably at least 5 meters, more preferably at least 10 meters.

With this kit, the length of the tube and hence of the stroke of the impact weight can be adjusted on site and to local conditions. For instance, if the driver is to be used at a depth of two kilometres, i.e. at a surrounding pressure of approximately 200 bar, a relatively short tube will be sufficient to decelerate the impact weight.

The invention further pertains to a method of installing foundation elements, such as anchors or piles, in a ground formation and preferably in submerged condition, by means of a driver comprising a housing for accommodating and guiding a weight, an element for mounting the driver on or in a foundation element, and a source for supplying a high pressure gas, such as a pyrotechnic charge, which method comprises the steps of

mounting the driver on or in a foundation element,

arranging a weight, such as a solid weight or water taken from the surroundings, in the housing,

releasing high pressure from the source to below the weight,

allowing the weight to rise (relative to the downward moving housing) and the gas to expand to such an extent that the gas causes the weight to decelerate, preferably to expand to a pressure at which the force exerted by the gas below the weight is lower than the sum of the weight (in N) and the downward force exerted on the weight by the medium present above the weight.

It is further noted that U.S. Pat. No. 4,060,139 relates to an underwater gas discharge type hammer with a gas reservoir into which expanded ram driving gas exhausts to avoid aeration of incoming water which surrounds the gas discharge device of the hammer. The gas reservoir is also arranged as a diving bell to minimize pressure changes under the hammer ram and thereby to maximize ram stroke and improve sharpness of ram impact on the hammer anvil.

U.S. Pat. No. 3,958,647 relates to a pile driver, which includes a cylindrical housing, a movable massive weight within the housing, an annular cylindrical thrust-transferring member defining a discharge chamber below this weight, and a movable driving head attached to this annular member, forming a thrust-transmitting assembly adapted to be engaged with the pile. Pressurized gas such as compressed air is discharged from a gas discharge apparatus, called an airgun located within the discharge chamber and provides two driving thrusts for each discharge. Through discharge passages (70), the released high-pressure gas, which may be intermixed with water in the discharge chamber, is permitted to escape, thus allowing the massive weight to move downwardly.

It will be understood that the terms “upward”, “downward”, “below”, “above”, and the like as employed herein, are not restricted to the driving of foundation elements vertically. The invention is also useful where the foundation elements are to be installed in angled or, depending on the configuration of the driver and the surrounding conditions, even horizontal orientations.

The invention will now be explained in more detail with reference to the figures, which show preferred embodiments of the driver according to the present invention.

FIGS. 1A to 1C show respectively a side view, a cross-section and a detail of that cross-section of a preferred driver, comprising a solid impact weight and mounted on an anchor plate.

FIGS. 2A to 2C show respectively a side view, a cross-section and a detail of that cross-section of the driver shown in FIGS. 1A to 1C, mounted inside a hollow pile.

FIGS. 3A to 3C show respectively a side view, a cross-section and a detail of that cross-section of the driver shown in FIGS. 1A to 1C, using water as an impact weight.

FIGS. 1A to 1C show a preferred driver 1 for installing foundation elements, such as anchors or piles, in a ground formation. This driver 1 comprises a number of detachably connected elements, viz., from top to bottom, a housing 2 for control means, a tube 3 or tube-like body having a cylindrical bore 4, a power-pack 5, and a stabbing point 6 known in itself, with which the driver 1 is mounted on an anchor plate 7. As the housing 2 comprises a trough-channel 2A, the bore 4 communicates directly with the surroundings of the driver 1.

The tube 3 in turn comprises a plurality of detachably connected segments 8, in this case steel cylinders having an outer diameter preferably in a range of from 70 to 120 cm, e.g. 90 cm, a bore in a range of from 45 to 60 cm, e.g. 50 cm, and a length preferably in a range of from 2 to preferably no more than 12 m (so as to fit into a standard container), e.g. 6 m. Suitable means for detachably connecting the various elements and segments include, but are not limited to threaded connections, bayonet couplings, and flanges.

As shown in FIG. 1C, the power-pack 5 comprises a central manifold 9 and upper and lower cylindrical wall portions 10, 11, each having an outer diameter, bore and wall thickness corresponding to those of the segments 8. Both wall portions 10, 11 contain a plurality of chambers 12 for holding a pyrotechnical charge 13, e.g. twelve chambers distributed equidistantly over the cross-section of the wall. As a matter of course, the composition and size of each propellant charge can be adjusted as desired to provide the desired impulse shape (as to duration and magnitude) best suited to the geotechnical conditions at hand.

The chambers 12 are cylindrical and extend parallel to the central axis 14 of the driver 1. Each chamber 12 is provided, at its end remote from the manifold 9, with an igniter 15, which is connected to the control means in the housing 2. The other end of each of the chambers 12 communicates, via a respective radially extending non-return valve 16, with a central bore 17 extending coaxially with the central axis 14 of the driver 1.

The embodiment shown in FIGS. 1A to 1C further comprises a solid impact weight 18, which is made of e.g. forged steel, optionally provided with two gaskets 19 made of e.g. brass or plastic and allowing sufficient clearance for gas to slowly vent, and fits closely inside the bore 4.

During operation, the anchor plate 7 and the driver 1 are attached to each other e.g. on the deck of a ship and by means of a steel cable, and lowered together. Subsequently, the anchor plate 7 is placed on a ground formation and the driver 1 is placed on top of the anchor plate 7 in a manner known in itself. Once the anchor 7 and driver 1 are in place and have been allowed to penetrate under self-weight, a first charge 13 is ignited and resulting high-pressure gas flows from the respective chamber 12, through the respective non-return valve 16 to the central bore 17 below the impact weight 18. The expanding gas exerts and upward force on the impact weight 18, lifting the same, and a downward force on the stabbing point 6 and anchor 7.

The length of the tube 3 has been selected such that the impact weight 18 can rise to a height at which the force exerted by the expanding gas below the impact weight 18 drops to a value, which is lower than the sum of the impact weight (in N) and the downward force exerted on the impact weight by the medium present above the impact weight. As a result, the impact weight 18 will decelerate. If the driver is used in submerged condition, e.g. two kilometres below sea level, the pressure in the surroundings will be approximately 200 bar and the height at which the impact weight starts to decelerate will be relatively small. It is generally preferred that the force exerted by the expanding gas below the impact weight 18 be allow to drop to a value, which corresponds to at least 1 G, preferably at least 2 Gs, more preferably at least 4 Gs of additional deceleration of the impact weight. Depending on the configuration of the driver and depth, additional deceleration can reach values of e.g. 20 Gs.

After the impact weight has come to a stop, it is accelerated by gravity and the pressure of the medium over the impact weight, thus compressing the gas below the weight and applying a second blow to the anchor.

In this particular example, the driver 1 does not have a discharge valve for discharging the gas. Instead, the gas will gradually escape past the gaskets 19 and the weight 18, while the weight 18 oscillates inside the bore 4. When a sufficient amount of the gas has escaped, a second charge 13 is ignited and the above process is repeated until the anchor 17 has been installed at the desired depth in the ground formation.

After reaching final penetration, the connection between the plate 7 and the driver 1 is cut e.g. by an ROV.

FIGS. 2A to 2C show a second driver 1, similar to the driver shown in FIGS. 1A to 1C, only mounted inside a hollow pile 20 and provided with a closed housing 2 on its top end thus defining a sealed, i.e. at least substantially watertight, gas compartment 21 above the weight 18. The gas compartment 21 effectively functions as a spring, i.e. the gas, for instance air, above the impact weight 18 is compressed as the gas below the weight 18 expands and the weight 18 rises. As a result, deceleration is further increased.

Gas will gradually escape past the gaskets 19 and the weight 18, while the weight 18 oscillates inside the bore 4. Alternatively, the weight and/or the wall of the housing is provided with one or more through-holes, channels and/or non-return valves to equalize pressure in a more controlled manner and/or faster. E.g., the weight may comprise 4 to 10, preferably 6 to 8, e.g. 6 through-holes (not shown) having a diameter in a range from 4 to 12, e.g. 8 mm. When sufficient pressure has escaped from below the weight, a second charge is ignited and the process is repeated.

FIGS. 3A to 3B show a further preferred embodiment, especially suitable for use in a submerged condition. In this embodiment, water is employed as an impact weight, i.e. the solid weight (18) is omitted and the bore 4 is filled with water typically taken from the surroundings. When a first charge 13 is ignited and resulting high pressure gas flows from the respective chamber 12 to the central bore 17, the driver 1 and the foundation element move downward and the water in the bore 4 is lifted to a height where of the pressure of the expanding gas drops to a pressure which is lower than the pressure of the surrounding water. At that height, the water will accelerate downwards applying a second blow. Depending on the circumstances, the gas will either escape directly via the descending water or part of the gas will be compressed and escape after a few oscillations of the water.

Owing the fact that the tube 3 comprises two or more mutually detachable segments, the length of the tube 2 and hence the length of the stroke of the weight can be varied and, more specifically, adjusted to surrounding conditions. In general, the length of the tube 3 is inversely proportionate to the water depth at which the driving is carried out.

From the above examples, it will be clear that a voluminous and heavy damping structure is in principle not required and that the driver can be built relatively slender and kept relatively lightweight.

The invention is not restricted to the above-described embodiments, which can be varied in a number of ways within the scope of the claims. For instance, instead of chambers filled with a combustible charge, it is possible to use e.g. one or more connectors for connecting the driver to source of a high-pressure gas, such as a closed loop nitrogen system, which contains an accumulator and is re-pressurised by means of a high-pressure compressor. In case of the drivers shown in the above Figures, such connectors could be provided at the location or one or more of the non-return valves. 

1. Driver (1) for installing foundation elements, such as anchors (7) or piles (20), in a ground formation and preferably in submerged condition, comprising a housing (3) for accommodating and guiding a weight (18), an element (6) for mounting the driver (1) on or in a foundation element (7; 20), one or more chambers (12) for holding a charge (13) or one or more connectors for connecting the driver (1) to a source of a high pressure gas, and corresponding conduits (16, 17) allowing a high pressure gas to flow from the chamber(s) (12) or connector(s) to below the weight (18), characterized in that, the housing (3) is adapted to allow a stroke of the weight (18) having a length such that, during upward movement of the weight (18), the pressure of the gas drops to a value, which will cause the weight (18) to decelerate.
 2. Driver (1) according to claim 1, wherein the housing (3) is adapted to allow a stroke of the weight (18) of at least 2 meters, preferably at least 5 meters, more preferably at least 10 meters.
 3. Driver (1) according to claim 2, wherein the housing comprises a tube (3) or tube-like body for accommodating and guiding the weight (18).
 4. Driver (1) according to any one of the preceding claims, wherein the housing (3) comprises two or more mutually detachable segments (8), with which the length of the housing (3) can be varied.
 5. Driver (1) according to any one of the preceding claims, wherein the chambers (12) for holding a charge (13) extend in the axial direction of the driver (1) and are located within the wall of the housing (3).
 6. Driver (1) according to any one of the preceding claims, wherein the end of the housing (3) remote from the element (6) for mounting the driver (1) on or in a foundation element (7; 20) is in fluid communication with the surroundings of the driver (1).
 7. Driver (1) according to any one of the preceding claims, wherein the housing (3) contains a solid impact weight (18) capable of reciprocating movement within the housing (3).
 8. Driver (1) according to claim 7 when dependent on any one of claims 1-5, comprising a sealed compartment (21) between the impact weight (18) and the end of the housing (3) remote from the said element (6).
 9. Driver according to claim 8, wherein the weight (18) and/or the wall of the housing (3) is provided with one or more through-holes, channels and/or non-return valves.
 10. Driver (1) according to any one of the preceding claims, wherein the pressure of the gas drops to a value, which will cause the weight (18) to decelerate by at least 1, preferably at least 2 additional Gs.
 11. Kit of parts for assembling a driver (1) for installing foundation elements, such as anchors (7) or piles (20), in a ground formation and preferably in submerged condition, comprising two or more segments (8) for assembling a housing (3) of a selectable length for accommodating and guiding a weight (18), an element (6) for mounting the assembled driver (1) on or in a foundation element (7; 20), and a section (5) comprising one or more chambers (12) for holding a charge (13) and/or one or more connectors for connecting the driver (1) to a source of a high pressure gas, and corresponding conduits (16, 17) allowing a high pressure gas to flow from the chamber(s) (12) or connector(s) to below the weight (18).
 12. Kit according to claim 11, wherein the total length of the segments (8) is at least 2 meters, preferably at least 5 meters, more preferably at least 10 meters.
 13. Method of installing foundation elements, such as anchors (7) or piles (20), in a ground formation and preferably in submerged condition, by means of a driver (1) comprising a housing (3) for accommodating and guiding a weight (18), an element (6) for mounting the driver (1) on or in a foundation element (7; 20), and a source (12) for supplying a high pressure gas, which method comprises the steps of mounting the driver (1) on or in a foundation element (7; 20), arranging a weight (18) in the housing (3), releasing high pressure from the source (12) to below the weight (18), allowing the weight (18) to rise and the gas to expand to such an extent that the gas causes the weight (18) to decelerate, preferably to expand to a pressure at which the force exerted by the gas below the weight (18) is lower than the sum of the weight and the downward force exerted on the weight (18) by the medium present above the weight (18).
 14. Method according to claim 13, which is carried out in submerged condition and wherein the housing (3) is at least partially filled with water and this water serves as the weight.
 15. Method according to claim 13 or 14, wherein the pressure of the gas drops to a value, which will cause the weight (18) to decelerate by at least 1, preferably at least 2 additional Gs. 